It is now well-known that products used for detergents are mostly responsible for the presence of phosphorous in water: among these the effect of sodium tripolyphosphate (STPP), used as a builder, has been particularly studied.
It is also well known that many efforts have been made in research to find an alternative to polyphosphates. But the various solutions attempted have not always given satisfactory results in that, when the STPP is removed or decreased, the variations which occur in the final results of the washing process are greater than those which would have been expected because of the sole decrease of the sequestering power of the detergent matrix.
This is due to the fact that it is impossible to find out a product which possesses the multiple characteristics of STPP, i.e. control of water hardness, buffer action, dirt dispersion and prevention of re-depositing.
Among the builders, citric acid and its salts, zeolites, nitryltriacetic acid (NTA) or polymeric polycarboxylic acids are now used.
Citric acid and sodium citrate are the main builders used in detergent liquids as they are the only ones which do not interfere with the enzymes present. Their percentage in these formulations is around 1-2%.
They represent 5% of the total market of builders.
They have the advantage of being entirely biodegradable, non-toxic, of being highly compatible with the other components of detergents and of having an effect of synergism with other builders (for example zeolytes).
Their use is limited by their efficiency. Their effectiveness quickly decreases with the temperature increase (T&gt;50.degree. C.). They have lower sequestering and dispersion power than polyphosphates (STPP).
Zeolytes are used in powder formulations.
As far as their toxic effect on the environment is concerned, these products are acceptable. They do not present any risk for water and do not increase the BOD load in plants for the treatment of waste water, even if, being insoluble. They do leave large quantities of sediments and materials in suspension.
As far as their detergency is concerned, they have a good absorbing capacity with respect to colored substances and pigments given out by fabrics. Their effectiveness as ion exchangers increases with the temperature. On the contrary, their ion exchange kinetics are slow, they have no buffer action and no dispersion power.
They are used in combination with other builders.
Nitrilotriacetic acid (NTA), after being initially accepted as a possible substitute for STPP, was then almost completely abandoned because of the numerous environmental problems involved.
As far as its efficiency as a detergent is concerned, its power as a complexing agent is 1.5 times higher than that of STPP and its performance is almost double in formulations for cold water. It has a better buffer effect, it is a good re-depositing prevention agent. It improves the effectiveness of optical bleaches. It stabilizes foams and perborates. It does not hydrolize during the washing process. It increases the solubility of some anionic surface-active agents (LAS type), and it is compatible with other components. It has the disadvantage of decolorizing colored fabrics based on metal complexes and has the tendency to agglomerate.
The real reason for its being abandoned, however, is due to the high toxicological risks involved in its use.
Its biodegradability is extremely limited, and the slime used for its processing requires a long acclimatation period. The rate of this process seems too slow to be able to keep up with the high fluctuations of NTA concentration, thus preventing its complete removal. The situation becomes worse in the processing of sea water and generally when the water hardness and NTA concentration increase.
The degradation of NTA is very limited also under anaerobic conditions. The above situation can have serious consequences: penetration and pollution of the water-tables damage to phytoplancton which cannot survive NTA concentrations higher than 1000 micrograms/liter with a risk of interrupting the feedingchain. The formation of complexes with the heavy metals present in the sediments, which go back again into solution, increase the risk of genetical changes and tumors.
The most valid polymeric polycarboxylic acids have been proved to be copolymers made up of acrylic acid and maleic anhydride.
These products are good complexing agents, they have a good dispersion and re-depositing prevention capacity, they improve the structure of the detergents by preventing the formation of lumps.
The main problem which limits their use is associated with their lack of biodegradability. It seems that polycarboxylates are accepted in Europe because they are protected by German legislation, for which it is sufficient for builders to be eliminated from water but not necessarily from the environment. This means that products are accepted which are not biodegradable (and thus cannot be eliminated from the environment) but are absorbed into the membranes of bacteria and in this way, eliminated from water.
It is precisely the biodegradability which stimulated further research on an alternative detergency. This brought about the study of copolymers of maleic anhydride and/or acrylic acid with natural substances such as starch or dextrine, copolymers of maleic anhydride and substances capable of introducing allylic and vinylic groups, copolymers of maleic anhydride/ethylene oxide, copolymers of glyoxylic acid/formaldehyde, etc. However results are still far from reaching expectations. At present, most detergents contain between 2 and 4% of polymers, mainly acrylic/maleic polymers combined with other builders.
It is also known (English patent No. 1404814) that polyaminoacids can act as surface-active agents, in that they are obtained through a reaction between polyimidic derivatives and long-chain aliphatic amines. By controlling the type of chain of the latter or the degree of polymerization of the polyimide, it is possible to choose the final characteristics of the polyaminoacid under examination.
However, the products described in the English patent do not seem to have sufficiently high characteristics to enable them to be used diversely or in any specific way that has not been already indicated. These characteristics may be summarized as follows: biodegradability, non-toxicity, no irritating effects, high solubility in water which, together with the detergent properties, determine the applicability and versatility of use in subsequent formulations.